1. Field of the Invention
The present invention relates to a display device including a thin film transistor formed by a droplet-discharging method typified by an ink-jetting method and relates to a method for manufacturing the display device.
2. Related Art
A display panel including a thin film transistor (hereinafter also referred to as a TFT) over a substrate, which is so-called an active matrix display panel, has been conventionally manufactured by patterning various thin films according to a photolithography process using a photomask in the same way as a manufacturing technique of a semiconductor integrated circuit.
In other words, the TFT can be manufactured by forming the thin film pattern as follows. After applying resist all over the substrate, prebake is performed to the resist, and then an ultraviolet ray or the like is irradiated thereto in order to expose the resist and to form a resist pattern according to the photolithography process. After that, a film (a film formed of a semiconductor material, an insulating material, or a conductive material) existing in the part not to be the thin film pattern is etched a way using the resist pattern as a mask. Thus, the thin film pattern is formed.
When a glass substrate or a display panel is small, the patterning can be performed comparatively easily by an exposure apparatus. However, with the increase of the size of the substrate, it becomes impossible to expose the whole surface of the display panel in one exposure process. As a result, a method has been developed in which the whole surface of the substrate is exposed in such a way that the region with the photoresist applied is divided into several blocks and then the exposure is made to the respective blocks sequentially (for example, refer to Japanese Patent Document Laid-Open No. H11-326951).
In manufacturing a semiconductor device, it has been examined to employ a droplet-discharging apparatus to pattern a thin film and a wiring used in the TFT for the purpose of reducing the cost of the facility and simplifying the process.
Japanese Patent Document Laid-Open No. 2000-188251 discloses a technique for forming a film over a semiconductor wafer with the use of an apparatus that can discharge resist having a narrow line shape continuously from a nozzle in order to suppress the consumption of the liquid required to form the film.
The droplet may have a small diameter in order to form the TFT having the small size by the drop-discharging method according to Japanese Patent Document Laid-Open No. 2000-188251. For this purpose, the nozzle may have the small diameter. In this case, however, a composition of the discharging droplet is clogged in the top of the nozzle due to adhesion, drying, or solidification of the composition, and therefore it is difficult to discharge a constant amount of droplet stably and continuously. This causes problems of low throughput and low yield of the semiconductor device formed by using the TFT.